Position detectors designed to detect the position indicated by an indicator such as a finger or a pen are known. A variety of position detection methods including resistance film method, electromagnetic induction method, and capacitance method are applicable for such position detectors.
Of those various types, electromagnetic induction position detectors include a sensor and a position indicator as an indicator as disclosed, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-212973). The position indicator is, for example, an electronic pen that generates an electromagnetic induction signal. The electromagnetic induction position detection sensor includes a number of thin and long loop coils arranged in the X- and Y-axis directions on a substrate. A position indicated by the position indicator is detected by detecting the electromagnetic induction signal from the position indicator with the loop coils on the substrate.
Electromagnetic induction position detectors permit input of a position with relatively high definition, thus making them widely popular.
On the other hand, as a position detection method for an indicator (e.g., a finger or a pen-type position indicator (a capacitive pen)) for devices such as touch panels, capacitive position detectors have been developed intensively in recent years. The capacitive type can be divided into two types, namely, surface capacitive type and projected capacitive type. Both types detect the position of the indicator by detecting the change in capacitive coupling between the sensor electrode and the indicator. A position detector based on a method called the cross point capacitance method, a method that has evolved from the projected capacitive method, has also been proposed (see, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2011-3034)).
FIG. 14 illustrates an example of a sensor for a position detector based on cross point capacitance. The sensor of a cross point capacitance position detector includes a plurality of upper electrodes Ex arranged, for example, in the Y-axis (vertical) direction of the indication input surface and a plurality of lower electrodes Ey arranged, for example, in the X-axis (horizontal) direction, as illustrated in FIG. 14. The electrodes Ex and Ey are arranged at predetermined intervals and orthogonal to each other with a small spacing therebetween. In this case, predetermined capacitance Co (fixed capacitance) is formed at each of the intersections (cross points) of the electrodes Ex and the electrodes Ey.
Then, at a position where an indicator 100 such as a position indicator held by the user or a user's finger approaches or touches the indication input surface, capacitance Cf is formed between the indicator and the electrodes Ex and Ey at that position. The indicator 100 is connected to ground through the human body via given capacitance Cg. As a result, the charge between the upper and lower electrodes Ex and Ey at the position indicated by the indicator 100 changes because of the capacitances of Cf and Cg. A cross point capacitance position detector detects this change in charge, thereby identifying the position indicated by the indicator 100 on the indication input surface.
This change in charge is detected by a position detection circuit 101. The position detection circuit 101 uses, for example, the lower electrodes Ey as transmission electrodes and supplies a given transmission signal to one of the electrodes, and receives a reception signal from one of the upper electrodes Ex as reception electrodes, thus detecting the charge variation. The position detection circuit 101 switches the transmission electrode to be supplied with a transmission signal, and at the same time detects the change in current of the reception signal from the reception electrode, thus detecting the position indicated by the indicator.